Rubber compositions are typically used for tire treads which may be optimized for various rubber composition properties to promote three tire properties; namely, traction, rolling resistance and treadwear.
In this regard, typically desirable physical properties for tire tread rubber compositions may include, for example, hardness, modulus, hysteresis as indicated by rebound properties, tangent delta (Tan. delta) at 0.degree. C., and abrasion resistance as indicated by DIN abrasion values. Such physical properties are well known to those having skill in the rubber compounding art and, in general, are considered to be predictive of tire tread performance.
The phenomenon of reversion in the accelerated sulfur vulcanization of cis 1,4-polyisoprene (natural or synthetic) or other diene-based elastomers is undesirable. Reversion occurs when polysulfidic crosslinks deteriorate with time and temperature. Subsequently, this leads to a reduction in crosslink density and a deterioration of physical properties (lower modulus and higher hysteresis).
Accordingly, it remains desirable to utilize a reversion resistant additive in various rubber compositions.
In the description of this invention, the term "phr," where used herein, and according to conventional practice, refers to "parts of a respective material per 100 parts by weight of rubber or elastomer".
In the description of this invention, the terms "rubber" and "elastomer," if used herein, may be used interchangeably, unless otherwise prescribed. The terms "rubber composition," "compounded rubber" and "rubber compound," if used herein, are used interchangeably to refer to "rubber which has been blended or mixed with various ingredients and materials" and such terms are well known to those having skill in the rubber mixing or rubber compounding art.